Low inertia high thrust vibrator



June 30, 1970 F. R. ABBOTT 3,518,463

LOW INERTIA HIGH THRUST VIBRATOR Filed Aug. 26, 1969 2 Sheets-Sheet f3INVENTOR.

FRANK f?. ABBOTT ATTORNEYS United States Patent O 3,518,463 LOW INERTIAHIGH THRUST VIBRATOR Frank R. Abbott, San Diego, Calif., assignor to theUnited States of America as represented by the Secretary of the NavyFiled Aug. 26, 1969, Ser. No. 853,158 Int. Cl. H02k 33/00 U.S. Cl. 310-4 Claims ABSTRACT OF THE DISCLOSURE A thin non-magnetic sheet isreciprocable between the coplanar pole faces of two flat stators. Thepole faces of one stator is intermediate the pole faces of the other sothat iron bars embedded in the sheet will reciprocate between twoadjacent poles of the stator as an AC signal is applied. The result is amuch reduced mass of reciprocating parts and increased natural frequencyof oscillation without reducing the thrust of the vibrator.

STATEMENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION Early electrodynamic vibrators with sucientpower to vibrate the piston of a submerged transducer employ analternating current coil of wire suspended in a radial magnetic field.These structures require a large magnetic air gap and a correspondinglylarge permanent magnet or large direct current excitation eld windings.Considerable improvement was accomplished by embedding transformer ironbetween the turns of the windings as disclosed in U.S. Pat. 3,126,520 or3,353,040 and Aas shown schematically in cross section in FIG. 1. A discat one or both ends of a tubular cylinder can be pushed outwardlyagainst high hydrostatic pressure by the 4reciprocating motor shown. Twoof the three magnetic cores of the field or stator structure areattached together and to the casing and the remaining core of thearmature structure is attached to the piston. Heavy conductors are-wound between the pole pieces and when energized by large 10W voltagefield currents and by alternating signal current the piston reciprocate.The bellows functions as a spring -Which is adjusted statically to holdthe AC poles at mid position between the DC poles. With an associatedspring constant, K, and an armature mass M, the practical minimumresonant frequency, F, of the oscillating assembly is:

The object of this invention is to lighten the armature of a vibratorand to increase the resonance frequency F of the vibrator.

SUMMARY OF THE INVENTION The objects of this invention are attained byreducing the mass, M, of the movable armature in the above formula so asto increase the frequency F. The weight is reduced by replacing therather massive core structure with a thin sheet of non-magnetic materialin which are embedded flattened laminated iron bars.

The field or stationary portion of said vibrator comprises two coreassemblies each with a plurality of uniformly spaced pole pieces, thefaces of said pieces being aligned and in parallel spaced planes, thepole faces of one "Ice core assembly being intermediate the pole facesof the other core assembly. The thin sheet with embedded barsreciprocates in the narrow space between pole faces when alternatingcurrent magnetizes the cores.

Other objects and features of this invention will become apparent tothose skilled in the art by referring to the preferred embodimentdescribed in the following specification and as shown in theaccompanying drawings in which:

FIG. 1 is a sectional view of a prior art vibrator;

FIG. 2 is a cross section of one vibrator according to this invention;

FIG. 3 is a planned view of the thin non-magnetic sheet employed as thereciprocable armature of the vibrator of FIG. 2; and

FIGS. 4 and 5 show the changing magnetic circuit of the stator andarmature of the vibrator of FIG. 2.

As stated, the prior art transducer, shown in FIG. l, comprises anarmature plate built up of relatively heavy pole pieces 17 interleavedwith the turns 21 of signal current windings. The spring constant of thebellows for the piston heads 12 is adjusted to normally hold the polepieces of the armature plate midway between the pole pieces 16 of thefield plate. As the signal current reverses, the direction of themagnetic pull on the armature reverses. The principal disadvantage ofthis structure is the considerable weight of the movable portions of thearmaturc.

In the specific embodiment of this invention shown in FGI. 2, the massof the reciprocating parts of the vibrator are materially reduced. Thecylindrical cage 10 is closed at one end with the piston head 21 and abellows as in the prior art. Two eld magnet cores 14 and 14A are eachprovided with a plurality of pole pieces 16 and 16A and are each fixedto the cage 10. The pole faces 18 of one core are smoothed and arecarefully aligned in a common plane as are the pole faces 18A of thepole pieces 16A of the other core. The windings 20 and 20A are wound inthe slots between the pole pieces and if connected to a direct currentsoruce will keep the alternate pole faces similarly polarizedmagnetically. The windings 20A wound about the pole pieces 16Aoppositely polarized pole faces 18A.

According to an important feature of this invention the magnetic andelectric circuits of the signal circuits of the vibrator are added tothe mass of the field structure where the direct current bias isprovided. The housing 10 is fixedly joined to the central core structurecomprising the windings 21 interspersed ywith the core pieces 17. Theturns of the windings 21 are preferably connected to an alternatingsignal source. However, the connections of the windings 20 and 21 todirect current and alternating current may be reversed, or as desired,divided in any manner with the sources.

The end faces 19 of the pole pieces 17 are disposed intermediate thepole faces 18 of the outer cores 14. Likewise, the end faces 19A areintermediate faces 18A. As the alternating signal current reverses, thepolarity of the faces of the core 17 reverses. If, say, the polarity oftwo adjacent pole faces 18 are positive and negative, or north andsouth, respectively, the near pole face of core 17 will alternately beattracted to one eld piece and then the other. Stated differently, astrong magnetic eld alternateis established between one end of core 17and the two adjacent ends of core 16. Likewise, magnetic attraction isalternatively established between any one face 19A and the two adjacentfaces 18A.

Now, the only movable portion of the assembly shown in FIG. 2 which willbe called the armature, are the thin sheets 25 and 25A of non-magneticmaterial such as any one of the commercial plastics with the requisitestrength and rigidity. Embedded in each sheet are spaced iron bars 23and 23A. The number of bars correspond to the number of pole pieces 17.The bars 23 are sufficiently wide, left to right in FIG. 2, tosubstantially cover one pole face 19 of core 17 and one only of twoadjacent pole faces 18 of the field magnet. This means that as thepolarity of the field coil 17 reverses the movable bar 23 shifts fromone fixed position over one pole face 18 to a position over the otherpole face 18. That is, as the magnetic polarity of the pole face 17reverses, the magnetic attraction of the pole face 19 will transfer atsignal frequency from one pole face 18 to the other which means that themovable bars 23 of the armature will shift to alternately cover one poleface 18 of one polarity or the pole face of the other polarity, as shownin FIGS. 4 and 5, respectively. The right hand edges of the two sheets25 may be cast integrally with or otherwise attached to the piston head12. By attaching the two sheets 23 symmetrically to the piston head 12,the piston is reciprocated in a straight line. Conveniently, the sheets25 and 25A may be spaced from the pole faces by thin shims or sheets oflubricating-type plastic such as Teflon.

According to another important feature of this invention the magneticbars 23 and 23A are fabricated with iron laminations as suggested inFIG. 3 from stampings corresponding in size and shape to the crosssection of the bars seen in FIG. 2. The stampings are adhesively joinedand are embedded in the plastic sheet 25 preferably in a castingtechnique.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A low intertia vibrator comprising:

a first core assembly having at least two pole pieces,

with coplanar pole faces,

a second core assembly lwith a pole piece having a pole face paralleltoo, spaced slightly from said coplanar pole faces and disposedintermediate the pole faces of said first assembly,

a thin sheet of non-magnetic material, reciprocable in the space betweenthe pole faces of said first and second assembly and adapted for drivinga reciprocable load,

an iron bar embedded in said sheet, said bar being flat and sufficientlywide in one dimension to overlay only one pole face of said firstassembly and the pole face of said second assembly,

means for oppositely magnetically biasing said two pole faces, and

means coupled to an alternating signal current for reversing at signalfrequency the magnetic polarity of said one pole face to alternatelyshift the position of the reciprocable thin armature.

2. In the low intertia vibrator defined in claim l, said first andsecond core assemblies each comprising an array of aligned, uniformlyspaced magnetic pole pieces, the faces of the pole pieces of one arraybeing coplanar and in closed spaces parallel relation with the coplanarfaces of the other array, said thin sheet of nonmagnetic material beingcoextensive in size and shape with said pole faces and reciprocablebetween the pole faces, and a plurality of magnetic bars embedded insaid sheet, l said bars being rectangular, elongated, parallel andspaced apart distances comparable to the spacing of said pole pieces,said arrays being relatively offset, so that one set 0f pole faces areapproximately opposite the spaces between the poles of the other array.3. A low inertia vibrator comprising, three interleaved plates Iwithopposed surfaces secured in fixed parallel spaced relation, the twoouter plates each comprising a magnetic core with a plurality of spacedpole pieces having coplanar pole faces in said opposed surfaces, themiddle plate comprising a plurality of separate rectangular spaced polepieces extending through the plate with the exposed faces disposedintermediate the pole faces in the opposed surfaces of the outer plates,a reciprocable sheet of non-magnetic material between each pair ofplates, from bars embedded in each sheet opposite the pole faces in themiddle plate, means for changing the magnetic polarity of the pole facesof the middle-plate pole pieces to magnetically contact said bars to aposition over the pole faces on either side of said middle-plate polepieces. 4. In the vibrator defined in claim 3, direct current windingsbetween the pole pieces of said outer plates, and alternating currentwindings between the pole pieces of said middle plate.

References Cited UNITED STATES PATENTS 1,871,446 8/1932 Decker 310-14 X3,149,255 9/1964 Trench 310-30 3,336,488 8/1967 Scott S10-30 X 3,366,8091/1968 Scott 310-28 X FOREIGN PATENTS 290,354 6/ 1965 Netherlands.

DONOVAN F. DUGGAN, Primary Examiner Y U.S. Cl. X.R.

